The Life-History and Anatomy of Butterflies 
himself more thoroughly and accurately as to the internal anat¬ 
omy of these insects may consult with profit some of the treatises 
which are mentioned in the list of works dealing with the sub¬ 
ject which is given elsewhere in this book. 
Polymorphism and Dimorphism. —Species of butterflies often 
show great differences in the different broods which appear. The 
brood which emerges in the springtime from the chrysalis, which 
has passed the winter 
under the snows, may 
differ very strikingly 
from the insect which 
appears in the second or 
summer brood; and the 
insects of the third or 
fall brood may differ 
again from either the 
spring or the summer 
brood. The careful stu¬ 
dent notes these differ¬ 
ences. Such species are 
called polymorphic, that 
is, appearing under dif¬ 
ferent forms. Some spe¬ 
cies reveal a singular 
difference between the 
sexes, and there may be 
two forms of the same 
sex in the same species. 
This is most common in 
the case of the female 
butterfly, and where 
there are two forms of 
the female or the male 
such a species is said to 
have dimorphic females 
or males. This phenomenon is revealed in the case of the 
well-known Turnus Butterfly; in the colder regions of the 
continent the females are yellow banded with black, like the 
males, but in more southern portions of the continent black 
females are quite common, and these dark females were once 
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